An alternate history...for the record, it requires a fair suspension of disbelief for some parts.
A Trotskyist in, let's say, the 2160s, decides that the mark of Stalin on socialism's history can't go unnoticed. So, he figures he'll do something about it. Acquiring a Luger and period-style clothing, he sends himself to 1918. As Stalin leaves a party meeting, he takes aim at his head and fires. Joseph Stalin thus dies before ever coming to power. A few nights later, he breaks into the Commissariat for War, and leaves designs for a certain rifle on Trotsky's desk: the AK-47.
He then returns to his own time, content and looking forward to what his changes entailed. Lenin still died in 1924, but Trotsky was never exiled, and rose to power. With the 'AK-18' as the standard issue rifle for the Red Army(The traveler credited Kalashnikov for the design.), and a military genius helming the Union, the Soviets advanced on the fascist Kingdom of Italy in 1928 and deposed Mussolini, giving him a public execution in Red Square in the name of socialism triumphing over fascism.
In 1935, the Soviets advance toward Berlin. With the superior design of the 'AK-18' at the disposal of the Red Army, the Karabiner-armed Nazis are thrown aside in their wake. With Western support once the Soviets scramble the forces towards the eastern approach towards the city, the Allies capture Hitler alive in 1936, and like Mussolini, he is given a public execution in Red Square. Utilizing captured German engineers and tools, several launch facilities are built near Vladivostok. In 1940, the Soviets bombard Hiroshima and Nagasaki with a hail of V-2 rockets.
While not doing the same amount of damage as the American atomic bomb would have, it was sufficient to force the Japanese government to capitulate. The Trotskyist Soviet Union still has the schism with the other Allies in Germany, leading to East Germany's establishment, along with the Warsaw Pact. Several other nations in Central and Eastern Europe hold a referendum on if to join. Attracted by the sight of what socialized economics did for several Nordic nations during the Depression, as well as effective Russian propaganda, Austria, Greece and Serbia join the Warsaw Pact in 1956.
The Soviets then turn their eye to their loyal ally to the south, Mongolia. Sending in an overwhelming force, the state is annexed to the Union in 1958. Fast forward to the late 1980s. The Soviet economy is struggling to maintain its progress towards true communism. Mikhail Gorbachev, the current General Secretary, is struggling to maintain power. Word breaks out among the people that he is planning to implement a market.
As most civilians see the state as very close to true communism at this point, they're outraged by this. A mixed force of soldiers and civilians storm the Kremlin. Gorbachev is dragged out and beaten to death by the crowd. The people then declare the nation a collectivist anarchy. Unfortunately, within months, infighting occurs between the different local councils, and finally, the collectivist Soviet Union collapses in the autumn of 1989.